Introduction to Programming
Chapter 4
432
Total Memory Clear
The complete memory can be cleared by positioning the cursor on the first
instruction of the program and then pressing [CLEAR MEMORY] 99. This
resets all the data table bits to zero. A total memory clear should be done
before entering the user program.
The program recommendations listed below for constructing a ladder
diagram rung should be considered.
NOTE: A condition instruction is defined as a nonblock input instruction.
Special considerations are given for multiply, divide and block
instructions. The rung size limitations exist because of the industrial
terminal screen size.
Only one output instruction can be programmed in a rung.
Program only one rung to energize an output device to simplify
troubleshooting and maximize safety.
Up to 12 condition instructions in series can be programmed in a rung.
Up to 11 condition instructions in series can be programmed in a rung if
the output is a multiply or divide instruction.
When the desired number of series conditions exceeds the horizontal
limit of the screen (Figure 4.16a), use a storage bit to make two rungs
(Figure 4.16b).
Up to 7 parallel branches can be programmed in a rung provided all the
inputs are condition instructions.
4.5
Program Recommendations
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